1. Field of the Invention
The present invention is related to a method and an apparatus for assisting diagnosis by physicians by analyzing the states of coronary arteries based on there dimensional data. The present invention is also related to a recording medium in which a program that causes at least one computer to execute the diagnosis assisting method is recorded.
2. Description of the Related Art
Apparatuses and software programs that analyze the states of organs and blood vessels based on three dimensional image data (volume data) obtained by CT (Computed Tomography) examinations are being provided as tools for assisting image diagnosis by physicians. Cardiac function analyzing functions and coronary artery analyzing functions are widely utilized as functions for assisting diagnosis of the heart. With respect to the cardiac artery analyzing functions, Japanese Unexamined Patent Publication No. 2009-195561 discloses an apparatus that extracts the intravascular regions and soft plaque candidates from a single three dimensional X ray CT image, and displays the extracted soft plaque regions overlapped on the three dimensional CT image.
A plurality of sets of volume data that represents the state of the heart at different points in time are necessary in order to understand the movement of the heart (temporal changes) when analyzing cardiac functions. For this reason, a plurality of sets of volume data having different phases within a single cardiac cycle are generally obtained during examinations of the heart. Meanwhile, the state of stenosis does not change dramatically within a single cardiac cycle. For this reason, analysis of coronary arteries is performed employing a single set of volume data, as described in Japanese Unexamined Patent Publication No. 2009-195561.
It is desirable to employ a set of volume data which is obtained when the movement of cardiac muscles is minimal when analyzing coronary arteries. Sets of volume data which are obtained when the movement of cardiac muscles is great often include problems, such as motion artifacts and faulty contrast caused by shifts in the injection timing of contrast agents, resulting in accurate extraction of coronary artery regions becoming difficult. Commonly, it is considered that sets of volume data obtained during a middiastolic state are favorable to be used for analyzing coronary arteries.
However, there are differences in the shapes of hearts and the movement of the cardiac muscles among individuals. In addition, the beating of the heart is accompanied by twisting of the cardiac muscles. Therefore, the movement of the cardiac muscles differs in the periphery of the left coronary artery and in the periphery of the right coronary in the same heart. For this reason, it is not always the case that a set of volume data that represents the heart in a middiastolic state is optimal as data to be utilized to analyze coronary arteries. In fact, there are reports that sets of volume data obtained during telesystolic states are favorable to analyze right coronary arteries and to analyze states during high heart rates. Therefore, it is difficult to determine a single optimal phase for analysis. Based on these circumstances, selection of volume data (selection of an optimal phase) to be employed to analyze coronary arteries is currently being performed based on visual evaluations by physicians and technicians.
As described above, it had been conventionally necessary to select one specific phase to perform coronary artery analysis. It is difficult for a computer to automatically select an optimal phase, and it had been necessary to rely on the visual evaluations of physicians and technicians. There is a problem that accurate evaluation results cannot be obtained if the selection of an optimal phase is erroneous. In view of these circumstances, it is an object of the present invention to provide an apparatus and a method which are capable of constantly accurately analyzing and evaluating the stenosis state of coronary arteries. It is another object of the present invention to provide a recording medium having a program, that causes at least one computer to execute the method of the present invention, stored therein.
A diagnosis assisting apparatus of the present invention is equipped with a volume data obtaining means, a coronary artery region extracting means, a correlation establishing means, an index value calculating means, an index value integrating means, and an output control means, as means for achieving the above objective. A coronary artery analyzing program which is stored in a recording medium of the present invention is a software program that causes one or a plurality of computers to function as the volume data obtaining means, the coronary artery region extracting means, the correlation establishing means, the index value calculating means, the index value integrating means, and the output control means. The coronary artery analyzing program is generally constituted by a plurality of program modules. The function of each of the means listed above is performed by one or a plurality of the program modules. The group of program modules is provided to users by being recorded in storage media such as CD-ROM's and DVD's, by being recorded in a storage unit attached to a server computer in a downloadable state, or by being recorded in network storage (non transitory storage) in a downloadable state. A coronary artery analyzing method of the present invention is a method that analyzes the states of coronary arteries, by executing the processes of the volume data obtaining means, the coronary artery region extracting means, the correlation establishing means, the index value calculating means, the index value integrating means, and the output control means, which will be described below.
The volume data obtaining means obtains a plurality of sets of volume data, each of which represent the state of a beating heart in different phases. In the case that the obtained sets of volume data are to be employed to analyze cardiac functions, it is preferable for the volume data obtaining means to obtain volume data which are generated and output by a modality, such as a CT apparatus, for all phases during a single cardiac cycle. Meanwhile, in the case that the obtained sets of volume data are to be employed only to analyze coronary artery functions, it is not necessary to obtain volume data for all phases, and volume data that represent phases within predetermined ranges may be obtained.
The coronary artery region extracting means extracts coronary artery regions from at least two sets of volume data from among the sets of volume data obtained by the volume data obtaining means. The coronary artery region extracting means may perform extracting processes with respect to all sets of volume data supplied by the volume data obtaining means. Alternatively, the coronary artery region extracting means may perform the extracting processes only with respect to sets of volume data that represent the states of specific phases, from among the sets of volume data supplied by the volume data obtaining means. It is preferable for the process to extract the coronary artery regions to be executed with respect to one or a plurality of sets of volume data that represents the heart in a telesystolic state, and one or a plurality of sets of volume data that represents the heart in a middiastolic state, from the viewpoint of analysis accuracy.
The correlation establishing means sets a plurality of analysis points in each of the extracted coronary artery regions, and establishes correlations among the analysis points, which are set at the same anatomical positions, within the plurality of coronary artery regions. The points which are set as analysis points may be those which are extracted by the coronary artery region extracting means as points that represent the paths of the coronary arteries, may be selected from among such points. Note that the expression “the same anatomical positions” refers to positions within ranges which are recognized as the same portions during diagnosis, and it is not necessary for the positions to match completely.
The index value calculating means calculates index values that indicate the character of plaque at each of the analysis points within all of the plurality of coronary artery regions. Here the expression “character of plaque” refers to whether plaque is present, the percentage occupied by plaque (stenosis rate), the properties of plaque (such as whether the plaque is unstable), components of plaque, etc. The index values are calculated based on at least one of the diameter, the area, and the signal values of either the coronary artery region, the intravascular regions of coronary arteries, or both. A plurality of index values will be calculated with respect to points which are at the same anatomical positions by the processes executed by the index value calculating means.
The index value integrating means evaluates the character of plaque at positions within the coronary artery regions, by integrating the index values which are calculated at the plurality of analysis points corresponding to each of the positions. For example, the index value integrating means may evaluate the character of plaque based on a total sum of a plurality of index values. Alternatively, the index value integrating means may calculate weighted averages of the plurality of index values by multiplying the index values by weighting coefficients which are set for each of the phases, and evaluate the character of plaque based on the values of the weighted averages. The index value integrating means evaluates the character of plaque based on a plurality of index values. Therefore, the influence imparted by inaccurate values to the evaluation results is lessened, even in cases that some of the plurality of the index values are inaccurate.
In the case that the weighted averages of the index values are calculated by the index value integrating means, it is preferable for the weighting coefficients that the index values calculated for analysis points corresponding to positions within a right coronary artery region are multiplied by to be set higher for the telesystolic phase than for other phases. Meanwhile, it is preferable for the weighting coefficients that the index values calculated for analysis points corresponding to positions within a left coronary artery region are multiplied by to be set higher for the middiastolic phase than for other phases. By setting the weighting coefficients in this manner, the influence imparted on the evaluation results by index values calculated from sets of volume data obtained during periods when the movement of the cardiac muscles is small can be relatively increased. Thereby, the accuracy of evaluations can be improved.
The output control means outputs the evaluation results regarding the character of plaque at each of the positions within the coronary artery regions, correlated with information regarding the positions. Recording of the evaluation results into recording media, and output of the evaluation results to a printer may be considered as manners in which the evaluation results are output, in addition of display on a screen. In the case that the evaluation results are displayed on a screen, it is preferable for the evaluation results for each position to be displayed such that they overlap images that represent the coronary artery region.
A configuration may be adopted, in which the diagnosis assisting apparatus further comprises alert required region detecting means, for detecting alert required regions based on the evaluation results regarding the character of plaque in addition to the aforementioned means. In this case, the output control means displays or prints the detected alert required regions in a discernable manner during output of the evaluation results. Here, the expression “alert required regions” refers to regions at which careful observation is thought to be required during diagnosis. In other words, the alert required regions are regions which have possibilities of being factors that may cause serious disorders. The alert required region detecting means may detect regions having index values that indicate a stenosis rate greater than a predetermined threshold value as alert required regions. Alternatively, the alert required region detecting means may detect regions having index values that indicate instability of plaque greater than a predetermined threshold value as alert required regions. Further, the alert required region detecting means may detect regions having index values that indicate a stenosis rate greater than a predetermined threshold value and index values that indicate instability of plaque greater than a predetermined threshold value as alert required regions. If the alert required region detecting means is provided, regions of interest can be focused on in advance, to reduce the burden of observations placed on physicians, thereby improving efficiency of diagnosis.
According to the present invention, it is not necessary to select specific phases to perform analysis. Accordingly, the burden of selecting phases is not placed on physicians or technicians. In addition, a plurality of sets of volume data that represent states in different phases are utilized to perform analysis. Therefore, the influence of sets of volume data having poor image quality can be reduced. As a result, great errors do not occur in the analysis results, and constantly uniform accuracy in analysis can be guaranteed.